Radio Frequency Identification (RFID) tags are used for many purposes, including article control in retail stores and warehouses, electronic toll collection, and tracking of freight containers. RFID tags, which include an antenna and a chip, may be attached to articles made of various types of materials, each type of material having different dielectric properties. The chip of the RFID tag may contain information uniquely identifying the article to which it is attached, where the article may be a book, a vehicle, an animal, an individual, or other tangible object.
An RFID tag antenna is typically designed for a specific chip, such as an application-specific integrated circuit (ASIC), and designed such that proper impedance match occurs between the antenna and the chip. In many cases, the RFID tag antenna is also designed for a specific high-dielectric material (e.g., a specific plastic) or a variety of low-dielectric materials (e.g., cardboard or wood), or use complicated structures where one geometrical parameter of the RFID tag antenna affects many of the other antenna parameters. RFID tag antennas are also designed with respect to specific frequency ranges.
Each country has adopted its own frequency allocation for RFID. In order for RFID equipment to be compliant with a particular country's allocated ultra-high frequency (UHF) regulations, the RFID system should be designed to operate within the country's specific frequency ranges. For example, Europe has an RFID UHF band of 866-869 MHz, North America and South America each have an RFID UHF band of 902-928 MHz, and Japan and some other Asian countries have an RFID UHF band of 950-956 MHz.
One challenge in RFID tag antenna design is the difficulty of creating an antenna that can be used on a variety of types of materials having different dielectric properties, particularly a variety of high-dielectric materials, such as different compositions of automobile glass. Another challenge is the difficulty of creating an antenna that can be used for a specific dielectric medium across all ultra-high frequencies. Thus, there is a need for an RFID antenna, which can be used across all UHF bands for a specific dielectric medium, or can be used in a single frequency band for different dielectric mediums.